This invention relates to an image processing apparatus that reads film images photoelectrically and which performs specified image processing schemes on the obtained image data to produce image data for output. More particularly, the invention relates to an image processing apparatus that has a capability for correcting uneven densities that occur in a frame of the image taken on a film with lens or using a compact camera or another inexpensive and low-performance camera, that is, shutter unevenness due to the shutter speed when shooting, reduction or deterioration of the image marginal luminosity (brightness at the edges of image field) due to the taking lens, and variation in the reduction of the marginal luminosity due to the stop-down value.
Heretofore, the images recorded on photographic films such as negatives and reversals (which are hereunder referred to simply as xe2x80x9cfilmsxe2x80x9d) have been commonly printed on light-sensitive materials (photographic paper) by means of direct (analog) exposure in which the film image is projected onto the light-sensitive material to achieve its areal exposure.
A new technology has recently been introduced and this is a printer that relies upon digital exposure. Briefly, the image recorded on a film is read photoelectrically, converted to digital signals and subjected to various image processing schemes to produce image data for recording purposes; recording light modulated in accordance with the image data is used to scan and expose a light-sensitive material to record a latent image, which is subsequently m developed to produce a finished print. The printer operating on this principle has been commercialized as a digital photoprinter.
In the digital photoprinter, images can be processed as digital image data to determine exposure conditions for printing, so various operations including the correction of washed-out highlights and flat (dull) shadows due to the taking of pictures with rear light or an electronic flash, sharpening, and the correction of color or density failure can be performed in an effective manner to produce prints of the high quality that has been unattainable by the conventional direct exposure. In addition, the assembling of images and the splitting of a single image into plural images, as well as the composition of characters can be performed by processing the image data and, as a result, prints can be output after various editing and/or processing operations have been performed in accordance with specific uses. Outputting images as prints (photographs) is not the sole capability of the digital photoprinter; the image data can be supplied into a computer or the like and stored in recording media such as a floppy disk; hence, the image data can be put to various non-photographic uses.
Having these features, the digital photoprinter is basically composed of the following units: an image input unit comprising a scanner (image reading apparatus) that reads the image on a film photoelectrically and an image processing apparatus that processes the captured image to produce image data for output (exposure conditions); and an image output unit comprising a printer (image recording apparatus) that records a latent image on a light-sensitive material by scan exposing it in accordance with the image data output from the image input unit and a processor (developing apparatus) that performs development and other necessary processing oh the exposed light-sensitive material to produce a print.
In the scanner, reading light issuing from a light source is allowed to be incident on a film, from which projected light bearing the image recorded on the film is produced and focused by an imaging lens to form a sharp image on an image sensor such as a CCD sensor; the image is then captured by photoelectric conversion and sent to the image processing apparatus as data for the image on the film (as image data signals) after being optionally subjected to various image processing schemes.
In the image processing apparatus, image processing conditions are set on the basis of the image data captured with the scanner and image processing as determined by the thus set conditions is performed on the captured image data and the resulting output image data for image recording (i.e., exposing conditions) are sent to the printer.
In the printer, if it is of a type that relies upon exposure by scanning with an optical beam, the latter is modulated in accordance with the image data from the image processing apparatus and deflected in a main scanning direction as the light-sensitive material is transported in an auxiliary scanning direction perpendicular to the main scanning direction, whereby a latent image is formed as the result of exposure (printing) of the light-sensitive material with the image bearing optical beam. In the processor, development and other processing, as determined by the light-sensitive material are performed in the processor to produce a print (photograph) reproducing the image that was recorded on the film.
In order to obtain high-quality prints, the image of a scene that was taken (i.e., the information about the image) is preferably recorded on a film as much as possible and in a faithful way. In fact, however, if the performance of the taking lens is not very high, it often occurs that the marginal luminosity is deteriorated as compared with the center of the image to thereby cause density unevenness in the image. This problem commonly referred to as xe2x80x9creduction of the marginal luminosityxe2x80x9d is particularly noticeable in a xe2x80x9cfilm with lensxe2x80x9d, or an integral photographic film and lens combination, since the rigorous cost restraints make it uneconomical to use a lens of very high performance. Further, the compact cameras have also the inevitable reduction of the marginal luminosity, because the lens performance is restricted by the cost restraints. As a result, the finished print has an image with dark edges, and the density unevenness is found in the image, leading to the deterioration in the image quality. There are three types of density unevenness, the first type is the reduction of the marginal luminosity due to the lens performance itself, the second type is the density unevenness associated with camera model (i.e., shutter type) and shutter speed, and the third type is the lens-dependent variation in the reduction of the marginal luminosity associated with stop-down value. Exemplary shutter types used in camera models include a pendulum-type shutter in the film with lens, a lens shutter in the compact camera, and a focal-plane shutter in the single-lens reflex camera.
Of these three types of density unevenness, there have been conventionally proposed, for the first type due to the lens performance itself, a number of methods for correcting deterioration in image quality. However, no effective method has heretofore been known to correct the density unevenness associated with camera model, shutter type and shutter speed as well as the variation in the reduction of the marginal luminosity associated with stop-down value.
The present invention has been accomplished under these circumstances and has as an object providing an image processing apparatus with which not only the heretofore correctable reduction of the marginal luminosity that is associated with lens performance itself but also the image density unevenness that is associated with shutter type and shutter speed, as well as variation in the reduction of the image marginal luminosity that is associated with stop-down value can be corrected to ensure consistent production of high-quality images that have no density unevenness nor darkness at the edges.
In order to achieve the above object, the inventor has made intensive investigations on the deterioration in the image quality of finished prints, and finally found that the method of correcting deterioration in image quality proposed by the inventor in U.S. Ser. No. 09/276,464 under the title xe2x80x9cimage processing apparatusxe2x80x9d is significantly effective for correcting the reduction of the marginal luminosity associated with taking lens performance itself, but that the proposed image processing apparatus cannot remove other types of image density unevenness in the frame that is caused by the shutter type and shutter speed, namely shutter unevenness and lens-dependent variation in the reduction of the marginal luminosity associated with stop-down value. The inventor has also found that these types of density unevenness are caused as follows:
FIG. 10 illustrates the operating principle of the simplest pendulum-type shutter, and FIGS. 11a and 11b show how the amount of exposure varies on the film image as the shutter moves. In FIG. 10, numeral 1 designates an optical path (lens), 2a refers to the shutter closing the optical path, and 2b refers to the shutter in a position clear of the optical path. Briefly, the shutter reciprocates between two states 2a and 2b so that the image on the film is subjected to a specified amount of exposure through the optical path 1. FIG. 11a shows four areas into which the film image is split, and FIG. 11b shows how the amount of exposure varies from one area to another at different shutter speeds (shadowed bars representing the lower-speed shutter). As is clear from FIGS. 10, 11a and 11b, the pendulum-type shutter causes uneven exposure of the film image, which leads to unevenness in the density of the image.
The same phenomenon occurs depending on the value to which the camera was stopped down during shooting. As FIG. 12 shows, if a high stop-down value is used (indicated by the dashed line and corresponding to the use of only the central area of the lens), greater reduction occurs in the marginal luminosity, again leading to unevenness in the density of the image.
The density unevenness that is associated with shutter speed or stop-down value is only about a fraction to a tenth of the density unevenness due to lens performance itself; however, in order to ensure consistent production of high-quality images, the former must also be corrected in an appropriate manner. The inventor has found that the former can be corrected according to the present invention in the same manner as the correction of the reduced marginal luminosity performed in the image processing apparatus proposed by the inventor in U.S. Ser. No. 09/276,464.
The present invention provides an image processing apparatus that captures an image on a photographic film photoelectrically to produce input image data and which performs specified image processing schemes on the input image data to produce output image data, said apparatus comprising:
an uneven density characteristics acquiring device in which uneven density characteristics associated with at least one of a camera model used to take the image of said photographic film and taking data are acquired; and
an image data correcting device for correcting said input image data in accordance with the thus acquired uneven density characteristics.
Preferably, said taking data include at least one of a shutter speed and a stop-down value in said camera model, and said uneven density characteristics are uneven density data in said image.
Preferably, said uneven density characteristics acquiring device previously includes:
a first storage device for storing said uneven density characteristics for each camera model used to take the image of said photographic film, or for each combination of the camera model with the taking data thereof, and
a device for acquiring information about said camera model used to take the image of said photographic film or information about said camera model and the taking data thereof, and said uneven density characteristics associated with said camera model or said camera model together with said taking data are read out of said first storage device, based on the information acquired about said camera model or said camera model and said taking data.
Preferably, said first storage device stores reference uneven density characteristics in a reference shutter speed for said each camera model, and said uneven density characteristics acquiring device further includes a device for calculating uneven density characteristics associated with the shutter speed from said reference uneven density characteristics when said shutter speed in said camera model is different from said reference shutter speed.
Preferably, said reference uneven density characteristics are reference uneven density data that are corrected for each image reading apparatus for reading the image of said photographic film.
Preferably, said image data correcting device includes:
a first device for developing said uneven density characteristics acquired by said uneven density characteristics acquiring device into a first light attenuation amount in accordance with a position of said image, and
a first density unevenness correcting device that subjects said input image data to a density unevenness correction of said image using said first light attenuation amount.
Preferably, said first device for developing said uneven density characteristics into said first light attenuation amount calculates the light attenuation amount in accordance with a distance from a center of said image due to said uneven density characteristics.
Preferably, said first density unevenness correcting device performs the density unevenness correction in said image using a distance from a center of said image and said first light attenuation amount.
Preferably, said image data correcting device changes a correction intensity of said density unevenness correction in accordance with a density of the photographic film of said image, decreases the correction intensity in a vicinity of a minimum density in the photographic film (e.g., a base density implying an unexposed area on a negative film, and a density defined as the fog area in a reversal film) or a maximum density in the photographic film(e.g., a density defined as the fog area in a negative film, and a base density implying an unexposed area in a reversal film), and increases the correction intensity as it gets farther away from the minimum density or the maximum density.
The image processing apparatus of the present invention further includes:
a device for acquiring information about said photographic film, and
a device for mutually converting a density of the photographic film and a taking light quantity using characteristics of the photographic film as obtained from the information about said photographic film, and is characterized in that said image data correcting device performs said density unevenness correction in a region having said taking light quantity.
Preferably, in prescan mode for reading said image at low resolution performed prior to image reading for producing said output image data, said image data correcting device performs said density unevenness correction before image analyzing processing including an auto setup process is performed, or after only a color balance adjustment included in said image analyzing processing is performed.
Preferably, said image data correcting device does not perform intensely said density unevenness correction in a vicinity of a minimum density or a maximum density about said image, intensely performs said density unevenness correction in a density region apart from the minimum density or the maximum density, and performs said density unevenness correction with an intermediate intensity in an intermediate density region.
The image processing apparatus of the present invention further includes:
a taking lens characteristics acquiring device for acquiring taking lens characteristics of the camera model used to take the image of said photographic film, and is characterized in that said image data correcting device further includes:
a second device for developing said taking lens characteristics acquired by said taking lens characteristics acquiring device into a second light attenuation amount in accordance with a position of said image, and
a second density unevenness correcting device that corrects density unevenness caused in a frame of said image due to reduction of marginal luminosity.
Preferably, said second device for developing said taking lens characteristics into the second light attenuation amount calculates the light attenuation amount in accordance with a distance from a center of said image due to said uneven density characteristics.
Preferably, said taking lens characteristics acquiring device includes:
a taking lens information acquiring device, and
a second storage device for storing said taking lens characteristics for each of information about a taking lens previously prepared, and said taking lens characteristics in accordance with the information about the taking lens obtained by said taking lens information acquiring device are read out of said second storage device.
Preferably, said first and second storage devices are composed of one memory, said first and second density unevenness correcting device are composed of one unit, and said first and second light attenuation amounts are added and used to subject said input image data to the density unevenness correction in said image.